Systems and methods for estimating time corresponding to peak signal amplitude

ABSTRACT

Various systems and methods for peak signal detection. As one example, a method for peak signal detection that includes receiving a signal is disclosed. The received signal includes a signal region where the signal is increasing in amplitude, another signal region where the signal is decreasing in amplitude, and a transitional signal region coupling the first two signal regions. In some cases, the transitional region is of zero duration and the signal transitions directly from the increasing region to the decreasing region. The method further include calculating a distance between the signal region of increasing amplitude and the signal region of decreasing amplitude, and determining a peak of the received signal that is one half the distance from the signal region of increasing amplitude.

BACKGROUND OF THE INVENTION

The present invention is related to storage media. More particularly,the present invention is related to systems and methods for preparingservo data on a storage medium.

A typical digital magnetic storage medium includes a number of storagelocations where digital data may be stored. Data is written to themedium by positioning a read/write head assembly over the medium at aselected location, and subsequently passing a modulated electric currentthrough the head assembly such that a corresponding magnetic fluxpattern is induced in the storage medium. To retrieve the stored data,the head assembly is positioned anew over the track. In this position,the previously stored magnetic flux pattern induces a current in thehead assembly that can be converted to the previously recorded digitaldata.

The storage locations on the magnetic storage medium are typicallyarranged as a serial pattern along concentric circles known as tracks.FIG. 1 shows a storage medium 100 with two exemplary tracks 150, 155 asdashed lines. The tracks are segregated by servo data written withinwedges 160, 165. These wedges include data and supporting bit patternsthat are used for control and synchronization of the head assembly overa desired storage location on storage medium 100. The data andsupporting bit patterns used to derive the control and synchronizationis depicted as a pattern 110 that includes a preamble 152, a sync 154, agray code 156 and a burst 158. It should be noted that while two tracksand two wedges are shown, hundreds of each would typically be includedon a given storage medium.

Traditionally, the servo data within wedges 160, 165 has been written byan external servo writer which is costly both in terms of equipment andtime. In some cases, disk drive manufacturers have utilized theread/write head assembly to write the servo data using a process knownas self servo writing. As one example of this process, an externalwriter is used to write servo data for only a limited number a tracks atan outer edge 190 of storage medium 100. Using this as a guide, the headassembly can then be used to write the servo data corresponding to theinner tracks. As another example, a reference pattern is applied moregenerally to storage medium 100 in a known way, but not correspondingdirectly to wedges 160, 165. While both approaches offer viablealternatives to the traditional approach, each requires additionalcapability for positioning the head assembly.

Hence, for at least the aforementioned reasons, there exists a need inthe art for advanced systems and methods for head assembly positioningduring self servo writing.

BRIEF SUMMARY OF THE INVENTION

The present invention is related to storage media. More particularly,the present invention is related to systems and methods for preparingservo data on a storage medium.

Some embodiments of the present invention provide methods for peaksignal detection. The methods include receiving a signal. The receivedsignal includes a signal region where the signal is increasing inamplitude, another signal region where the signal is decreasing inamplitude, and a transitional signal region coupling the first twosignal regions. In some cases, the transitional region is of zeroduration and the signal transitions directly from the increasing regionto the decreasing region. The methods further include calculating adistance between the signal region of increasing amplitude and thesignal region of decreasing amplitude, and determining a peak of thereceived signal that is one half the distance between the two signalregions.

In some instances of the aforementioned embodiments, the signal regionof decreasing amplitude is substantially symmetric with the signalregion of increasing amplitude. In such instances, calculating thedistance between the two signal regions may include determining a slopeof the increasing amplitude and the slope of the decreasing amplitude,and determining an intercept between the slope of the increasingamplitude and the slope of the decreasing amplitude.

In other cases, calculating the distance between the two signal regionsmay include storing a plurality of sequential samples received from theregion of increasing amplitude, and another plurality of sequentialsamples received from the region of decreasing amplitude. The pluralityof samples from the two regions are compared on a sample by sample basisin reverse order. The plurality of samples from the region of decreasingamplitude is repeatedly updated with additional samples that arecompared with those from the region of increasing amplitude at leastuntil a minimum difference between the sample sets is identified. Inparticular cases, a first time is associated with the sample set fromthe increasing amplitude region and a second time is associated with thesample set from the decreasing amplitude region. From these, a time tothe peak or center of the signal is determined. In some cases, digitalinterpolation is applied to the signal to create the sets of sequentialsamples. In other cases, a time recovery loop is applied such that asample clock used to retrieve the samples from the signal issynchronized with the peaks of information maintained in the signal.

In some instances of the aforementioned embodiments, the methods furtherinclude providing a storage medium that includes a spiral referencepattern thereon. In such instances, receiving the signal includestraversing the storage medium along a traversal path that crosses thespiral reference pattern at an angle greater than zero. In suchinstances, the region of increasing amplitude occurs in relation to anincreasing cross-over with the spiral reference pattern and the regionof decreasing amplitude occurs in relation to a decreasing cross-overwith spiral reference pattern. The transitional signal region occurs inrelation to a substantially constant cross-over with the spiralreference pattern. In some cases, the angle at which the traversal pathcrosses the spiral reference pattern is programmable through the powerof placing the spiral reference pattern on the storage medium.

Other embodiments of the present invention provide systems for writingservo data. Such systems include a spiral entry locator circuit that isoperable to detect an entry cross-over of a spiral reference pattern,and a spiral exit locator circuit that is operable to continuouslydetect an exit cross-over of the spiral reference pattern. In addition,the systems include a comparator that is operable to determine a minimumdifference between an output of the spiral exit locator circuit and anoutput of the spiral entry locator circuit. A location calculator isincluded that is operable to determine a location corresponding to apeak of the spiral reference pattern.

In some instances of the aforementioned embodiments, a storage medium isprovided that includes a spiral reference pattern. In such instances,the spiral entry locator circuit receives a signal from a head assemblytraversing the storage medium along a traversal path that crosses thespiral reference pattern at a non-zero angle. As the head beginstraversing the spiral reference pattern the spiral entry locator circuitidentifies a region of increasing signal amplitude. Further, as the headtraverses the path away from the spiral reference pattern, the spiralexit locator circuit identifies a region of decreasing signal amplitude.

In one particular instance of the aforementioned embodiments, the spiralentry locator circuit includes a programmable sample number. In such aninstance, the spiral entry locator circuit is further operable to storea sequence of samples corresponding to the programmable sample numberfrom an entry region of the spiral reference pattern. In some cases, thespiral entry locator circuit is further operable to store anothersequence of samples corresponding to the programmable sample number froman exit region of the spiral reference pattern.

Yet other embodiments of the present invention provide methods foridentifying servo data locations on a storage medium. The methodsinclude providing a storage medium that includes a spiral referencepattern, and traversing the storage medium along a traversal path. Thetraversal path crosses the spiral reference pattern at a non-zero angleand results in receiving a signal. The received signal includes a regionof increasing amplitude, a region of decreasing amplitude and atransitional region there between. In some cases, the transitionalregion is of zero duration and the signal transitions directly from theincreasing region to the decreasing region. The methods further includeidentifying a location in the region of increasing amplitude and acorresponding location in the region of decreasing amplitude. A time isfixed for the location in the region of increasing amplitude and anothertime is fixed for the location in the region of decreasing amplitude.Based at least in part on the fixed times, a distance between thelocations is calculated, and a peak of the signal is determined.

This summary provides only a general outline of some embodimentsaccording to the present invention. Many other objects, features,advantages and other embodiments of the present invention will becomemore fully apparent from the following detailed description, theappended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the various embodiments of the presentinvention may be realized by reference to the figures which aredescribed in remaining portions of the specification. In the figures,like reference numerals are used throughout several drawings to refer tosimilar components. In some instances, a sub-label consisting of a lowercase letter is associated with a reference numeral to denote one ofmultiple similar components. When reference is made to a referencenumeral without specification to an existing sub-label, it is intendedto refer to all such multiple similar components.

FIG. 1 depicts a known storage medium;

FIGS. 2 a-2 c graphically depict a method for writing servo data using aspiral reference pattern in accordance with one or more embodiments ofthe present invention;

FIG. 3 is a flow diagram showing a method for writing servo data inaccordance with some embodiments of the present invention;

FIGS. 4 a-4 e show a system for writing servo data using a spiralreference pattern in accordance with various embodiments of the presentinvention; and

FIG. 5 depicts a low pass filter that may be used in relation to one ormore embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to storage media. More particularly,the present invention is related to systems and methods for preparingservo data on a storage medium.

Turning to FIG. 2 a, a storage medium 200 is depicted with a spiralreference pattern 210 formed thereon. In one particular case, the spiralreference pattern includes a repeating pattern of a preamble and servoaddress mark. In addition, two tracks 250, 255 are also shown on storagemedium 200 as dashed lines. Tracks 250, 255 may be formed as concentriccircles on storage medium 200 at known distances from an outer edge 205of storage medium 200. The data stored on storage medium 200 may beserially arranged along tracks 250, 255. It should be noted that a muchlarger number of tracks may be used in accordance with embodiments ofthe present invention and that the depiction of only two tracks isintended to simplify the description.

As shown, spiral reference pattern 210 extends in a smooth spiral shapefrom an outer edge 205 of storage medium 200 to an inner edge 295 ofstorage medium 200. In some cases, spiral reference pattern 210 isformed when the head of an external servo writer writes a repeatingpattern as storage medium 200 is rotated at a constant rate and the headof the external servo writer is moved from outside edge 205 to inneredge 295 also at a constant rate. Using such an approach, anycircumferential location along spiral reference pattern 210 is afunction of distance from outer edge 205. Based on the disclosureprovided herein, one of ordinary skill in the art will recognize otherapproaches that may be utilized for forming spiral reference pattern210.

Track 250 intersects spiral reference pattern at a location 240, and anangle 270. Track 255 intersects spiral reference pattern 210 at alocation 230, and an angle 280. The angle at which a track intersectsspiral reference pattern 210 is a function of the number of revolutionsincluded in spiral reference pattern from outer edge 205 to inner edge295 and in some cases can be programmed at the time spiral referencepattern 210 is written on storage medium 200. As shown, spiral referencepattern 210 makes approximately two revolutions around storage medium200 resulting in relatively large angles 270, 280. However, spiralreference pattern 210 is merely exemplary and it should be noted thatspiral reference pattern 210 may make many more revolutions as itprogresses from outer edge 205 to inner edge. This increase inrevolutions results in a corresponding decrease in angles 270, 280. Insome embodiments, the number of revolutions is high and thecorresponding intersection angles are close to zero, but still non-zero.

Turning to FIG. 2 b, an exemplary wedge 275 extending from an edge 273to another edge 277 is included as part of storage medium 200. Wedge 275can be one of many wedges distributed like spokes of a wheel across thecircumference of storage medium 200. Wedge 275 may be written with astandard servo data pattern including a preamble, a sync, a gray codeand a burst. In accordance with some embodiments of the presentinvention, this servo data pattern may be written at locations alongparticular tracks using spiral reference pattern 210 as a locationguide. In particular, a location for servo data within wedge 275 may bedefined as a distance, D1, from intersection point 240, or a distance,D2, from intersection point 230. In some cases, D1 and D2 are measuredas times where storage medium 200 is rotated at a known rate.

In an exemplary operation, storage medium 200 is provided with spiralreference pattern 210 formed thereon. Storage medium 200 is installed ina disk drive that includes a read/write head assembly disposed near thesurface of storage medium 200. Storage medium 200 is rotated in relationto the head assembly. As storage medium 200 rotates, the head assemblytraverses along a traversal path that intersects spiral referencepattern 210 at particular intersection locations depending upon thedistance of head assembly from outer edge 205. By detecting theintersection location, the distance of the head assembly from outer edge205 can be determined, along with a circumferential location relative toa starting point 204 of spiral reference pattern 210. Based on thisinformation, the location of the head assembly can be adjusted inrelation to outer edge 205 such that it is disposed over a selected oneof tracks 250, 255. In addition, storage medium 200 can be rotated suchthat the head assembly is located at one of the edges 273, 277 of wedge275. Thus, for example, where servo data is to be written as part oftrack 255 at wedge 275, the head assembly can be positioned at edge 273where it intersects track 255. From this location, storage medium 200 isrotated at a known rate such that the head assembly traverses a portion218 of track 255. As the head assembly traverses portion 218, amodulating electric current is passed through the head assembly causingthe servo data to be written along portion 218. This process is repeatedfor the other wedges (not shown) that are distributed on the surface ofstorage medium 200, and for other tracks also distributed on the surfaceof storage medium 200.

To write the servo data properly, it is desirable to accurately detectthe intersection with spiral reference pattern 210 such that the headassembly may be properly positioned within the wedge to be written. Insome embodiments of the present invention, the location of theintersection is defined as approximately the median amount of time thatthe head assembly is in a position to detect the spiral referencepattern as storage medium 200 is rotated.

This process of detecting the intersection with spiral reference pattern210 is further described in relation to FIG. 2 c. A traversal path 279indicates the path traversed from right to left by the head assembly asstorage medium 200 is rotated in relation thereto. As shown by traversalpath 279, the head assembly begins to intersect spiral reference pattern210 at an angle 271, and a location/time 212. At this point, the headassembly moving along traversal path 279 begins detecting spiralreference pattern 210, but the detected signal amplitude is relativelysmall due to the limited cross over between the head assembly and thespiral reference pattern. As the head assembly continues, the cross overwith spiral reference path 210 increases and causes a correspondingincrease in the detected signal amplitude. This increase in detectedsignal amplitude is graphically depicted as a region 229 of increasingamplitude of an overall detected signal pattern 219. The detected signalamplitude continues to increase until a location/time 222 where the headassembly is entirely over spiral reference path 210. A transitionalregion 239 is traversed where the detected signal amplitude remainssubstantially constant. This continues until a location/time 232 wherethe head assembly begins to move away from spiral reference path 210. Asthe head assembly moves away from spiral reference path 210, theamplitude of the detected signal begins to decrease. This results in aregion 249 of decreasing signal amplitude. Such a traversal of spiralreference pattern 210 along traversal path 279 results in a symmetry ofoverall detected signal pattern 219.

As will be appreciated by one of ordinary skill in the art based on thedisclosure provided herein, the shape of overall detected signal pattern219 may be changed where one or more variables are modified. Thedepicted “submarine” shape may assume more of “football shape” or moreof a “diamond” shape or “elongated diamond” shape as one or morevariables is/are modified. For example, where intersection angle 271 isincreased, the length of time that the head spends traversing spiralreference pattern 210 is decreased causing the rate of the increase inamplitude at region 229 and the rate of decrease in amplitude at region249 to accelerate. In addition, the length of transitional region 239 isdecreased. In some cases, the length of transitional region 239 isreduced to zero. In such cases, transitional region 239 is an immediatetransition of zero length from an area of increasing amplitude to anarea of decreasing amplitude. As another example, where the area that isdetectable by the head assembly is narrowed (i.e., traversal path 279 isnarrower), the length of overall detected signal pattern 219 isdecreased. Further, it should be noted that overall detected signalpattern 219 is shown with exemplary repetition of the signal written aspart of spiral reference pattern 210, but that many more repetitions arecommon within region 229 and region 249. Thus, where approximately twopeaks are shown in each of regions 229, 249, an actual detected signalmay include ten or more peaks within each region.

Traversal of spiral reference pattern 210 by the head assembly isaccomplished in a period T-Total which is affected by the rate at whichstorage medium 200 is rotated in relation to the head assembly. PeriodT-Total includes a period T-Left consumed in traversing region 229, aperiod T-Center consumed in traversing transitional region 239, and aperiod T-right consumed in traversing region 249. In particularembodiments of the present invention, the half way point of periodT-total is calculated. This mid-way point is referred to as peak timemark 390 and may be used as the intersection point for determininglocations within wedges to be written with servo data. Such an approachoffers increased accuracy when compared with simply detecting anyintersection with spiral reference path 210. In addition, the accuracyis not lost where angle 271 is increased or decreased, or where thewidth of traversal path 279 is modified.

In some embodiments of the present invention, determining peak time mark390 includes identifying a signal portion associated with region 249that exhibits a similar amplitude as known portion of region 229, andcalculating the mid-point between the respective signal portions. Thismay be represented in time by added a time associated with the portionof region 229 to the time associated with the portion of region 249, anddividing in half. This approximate mid-point serves as an accuraterepresentation of the location of spiral reference pattern 210, and canbe used for identifying appropriate locations for writing the variouswedges.

Turning to FIG. 3, a flow diagram 400 illustrates a method in accordancewith one or more embodiments of the present invention for identifyingpeak time mark 390 as discussed above. Following flow diagram 400, a lowpass filtered signal is received (block 405). The system continues toreceive low pass filtered signals until the distinctive increase inamplitude corresponding to region 229 is detected (block 410). Once itis determined that the detected signal is within region 229 (block 410),a programmable number (i.e., “N”) of consecutive samples of the detectedsignal are captured (block 415), and a time associated with the detectedsamples is stored (block 420). The samples from region 229 are generallyreferred to as reference samples.

With the reference samples of region 229 captured (block 415), a delayperiod is started (block 423) and the period of the delay is waited(block 425) to avoid comparison of the reference samples from region 229with later samples that may result in a false indication that anappropriate point in region 249 has been achieved. Once the delay periodhas expired (block 425), another set of “N” consecutive samples iscaptured (block 430) and compared with the previously captured referencesamples (block 435). This comparison is done on a on a sample by samplebasis and in reverse order. The reverse order of the comparison accountsfor the fact that the reference samples are captured in region 229 wherethe amplitude is increasing, and the purpose of the comparison is toidentify a reasonably close set of samples from region 249 where theamplitude is decreasing. The sum of absolute errors from the comparisonis stored for the comparison along with a time corresponding to thesamples (block 440).

In the next sample period, one or the recently captured “N” samples isreplaced with a new sample in FIFO order (block 445). This newlyconstituted set of samples is compared with the reference samples usingthe same approach as described in block 435 (block 450). Where the newlycomputed comparison error is less than the previously stored comparisonerror (block 455), the newly computed comparison error replaces theprevious comparison error and a time stamp associated with the newlycomputed comparison error is stored as time T2 (block 460).Alternatively, where the newly computed comparison error is greater thanthe previously stored comparison error (block 455), the previouslystored comparison error is retained.

It is determined whether the head assembly is still traversing spiralreference pattern 210 (block 465). Where the head assembly is stilltraversing spiral reference pattern 210 (block 465), the next detectedsignal is received and the process of blocks 445-465 is repeated.Alternatively, where the head assembly has moved beyond spiral referencepath 210 (block 465), peak time mark 390 is computed by averaging timesT1 and T2. This approximate mid-point serves as an accuraterepresentation of the location of spiral reference pattern 210, and canbe used for identifying appropriate locations for writing the variouswedges. At this point, the process returns to the beginning to await thenext intersection with spiral reference pattern 210.

Turning to FIGS. 4, a system 300 for detecting an approximate mid-pointof the traversal region is discussed. As shown, system 300 includes anotch filter circuit 310, a bandpass filter circuit 320, a spiral entrydetector circuit 330, a phase synchronization circuit 340, a spiral exitlocator circuit 350, a comparator circuit 360, and a locationcalculation circuit 370. In operation, a detected signal 380 is receivedfrom a read/write head assembly reading storage medium 200 alongtraversal path 279. Detected signal 380 is passed through both bandpassfilter circuit 320 and notch filter circuit 310. Notch filter circuit310 is operable to isolate energy at frequencies other than thefrequency exhibited by spiral reference pattern 210. In contrast,bandpass filter circuit 320 is operable to isolate energy at thefrequency exhibited by spiral reference pattern 210.

In some embodiments of the present invention, notch filter circuit 310is a digital filter that has a null at the frequency of the informationrecorded as part of spiral reference pattern 210, and uses the followingdigital frequency coefficients: 1, 0, 0, 0, −1. In various embodimentsof the present invention, bandpass filter circuit 320 is a digitalfilter that uses the following digital frequency coefficients: 1, 1, −1,−1, 1, 1, −1, −1. Based on the disclosure provided herein, one ofordinary skill in the art will recognize other filter coefficientsand/or filter types that may be used in accordance with one or moreembodiments of the present invention. For example, bandpass filtercircuit 320 may be a longer filter than that represented by theaforementioned coefficients.

The respective outputs from bandpass filter circuit 320 and notch filtercircuit 310 are provided to spiral entry locator circuit 330. In turn,spiral entry locator circuit 330 compares the received filter outputs,and time averages the comparison to determine whether detected signal380 is within region 229 where the detected signal amplitude isincreasing. Said another way, spiral entry locator circuit 330determines if the head assembly is beginning to traverse spiralreference pattern 210 as indicated by an increase in energy at or nearthe frequency of data recorded in spiral reference pattern 210.

Once region 229 has been identified, spiral entry detector circuit 330stores two or more samples separated by a determined time. Storing thesamples can include flushing the latency of bandpass filter circuit 320before to access the appropriate sample value from the filter output.These samples serve as reference samples corresponding to region 229 ofoverall detected signal pattern 219. The number of samples and thesampling period may be user programmable to accommodate different ratesof increase and decrease of amplitude in region 229 and region 249respectively, and different lengths of overall signal pattern 219.

To increase the accuracy of the samples and thereby the accuracy ofsystem 300, phase synchronization circuit 330 adjusts the phase ofeither the sample clock or the data such that the samples correspond tothe peaks of the data read from spiral reference pattern 210. This maybe done asynchronously through use of a digital interpolator tointerpolate detected signal 380 as received from an analog to digitalconverter as is known in the art. The digital interpolator producesdigital samples of detected signal 380 as filtered with a phase thatcorresponds to, for example, the positive peak value of the dataretrieved from spiral reference pattern 210. Examples of digitalinterpolators that may be used in accordance with embodiments of thepresent invention are disclosed in V. Annampedu et al., “AdaptiveAlgorithms for Asynchronous Detection of Coded Servo Signal Based onInterpolation,” IEEE Trans. Magnetics, 2005. However, based on thedisclosure provided herein, one of ordinary skill in the art willrecognize a variety of digital interpolators and/or digitalinterpolation techniques that may be used in relation to embodiments ofthe present invention.

Alternatively, phase synchronization circuit 340 may implement atraditional timing recovery approach for synchronization. As an example,phase synchronization circuit 340 may be a phase lock loop circuitcapable of driving a clock used to sample detected signal 380 asfiltered such that the signal is captured at, for example, its positivepeak value for the data retrieved from spiral reference pattern 210.

In one particular embodiment of the present invention, three samplesseparated by a programmable time period are stored. Based on thedisclosure provided herein, one of ordinary skill in the art willrecognize an appropriate number of samples to store, as well as anappropriate sample period. Further, one of ordinary skill in the artwill appreciate an appropriate method for assuring that the phase atwhich the samples are captured is consistent across the samples, therebyyielding samples that are comparable on a sample by sample basis.

In some cases, the detected input is magnitude qualified before thefirst of the samples is recorded. This assures that only samples asufficient distance away from the zero energy point of region 229 thatare less susceptible to noise are stored. Once the samples are stored, atime is associated with the stored samples. This may be done, forexample, by taking the time that the second of three samples wasrecorded as the time for all three samples. Based on the disclosureprovided herein, one of ordinary skill in the art will recognize avariety of other methods that may be used to time mark the samples. Forexample, time may be established as zero where the first sample isstored.

Next, the time mark associated with the reference samples is provided tolocation calculator 370, the samples are provided to comparator 360, andprocessing turns to detecting the exit of traversal path 279 from spiralreference pattern 210 by spiral exit locator circuit 350. In someembodiments, spiral exit locator circuit 350 implements a delay that maybe less than the time that the head is expected to be entirely overspiral reference pattern 210 (i.e., T-Center from FIG. 2 c). This delayreduces the possibility that samples may be captured by spiral exitlocator circuit 350 that are very near those previously captured byspiral entry locator circuit 330. Samples of such close proximity maypossibly cause a false reading of region 249 by spiral exit locatorcircuit 350. In some embodiments, the delay time is programmable.

Once this delay has expired, spiral exit locator circuit 350 beginscollecting samples of detected signal 380 as filtered. These collectedsamples are provided to comparator circuit 360 where they are comparedwith the samples previously captured by spiral entry locator circuit 330on a on a sample by sample basis and in reverse order. Thus, forexample, where three samples (S_(IN1), S_(IN2), S_(IN3)) are captured byspiral entry locator circuit 330, at least three samples (S_(OUT1),S_(OUT2), S_(IN3)) are collected by spiral exit locator circuit 350.Comparing the samples in reverse order on a sample by sample basisincludes comparing S_(IN1), to S_(OUT3), S_(IN2) to S_(OUT2), andS_(IN3) to S_(OUT1). The reverse order of the comparison accounts forthe fact that the samples captured by spiral entry locator circuit 330are obtained in region 229 where signal amplitude is increasing, andwhen properly matched the samples captured by spiral exit locatorcircuit 350 are obtained in region 249 where signal amplitude isdecreasing.

The results of each of the comparisons is used to compute a sum ofabsolute errors, and a time mark is associated with the calculated sum.This process of sampling and comparison is repeated until theapproximate end of region 249 is identified. In particular, after adefined period, spiral exit locator circuit 350 shifts the previouslycaptured samples one sample space right, and captures the newest sample.Thus, for example, where S_(OUT1), S_(OUT2), S_(OUT3) represent thepreviously captured samples, spiral exit locator circuit 350 updates thesamples to be S_(OUTNEW), S_(OUT1), S_(OUT2). These three samples arecompared with the samples previously captured by spiral entry circuit330, a sum of absolute errors is calculated, and a time stamp associatedtherewith. In some embodiments of the present invention, only the timeassociated with the minimum absolute sum of errors is maintained. Thus,where the newly captured sample set has an absolute sum of errors thatis lower than the previous sample set, the time associated with thenewly captured sample set replaces the previously recorded time.Alternatively, where the newly captured sample set has an absolute sumof errors that is greater than or equal to that of the previous sampleset, the time associated with the previously captured sample set isretained.

Once sampling of overall detected signal pattern 219 is completed,location calculator 370 receives the time associated with the sample setprovided by spiral entry locator circuit 330 (hereinafter “T1”) and thetime associated with the minimum absolute sum of errors provided byspiral exit locator circuit 350 (hereinafter “T2”). Location calculator370 provides a peak time mark that is calculated as the average of theaforementioned two times less an implementation delay as set forth inthe following equation:Peak Time Mark=(T1+T2)/2−Implementation Delay.The implementation delay accounts for the delay through bandpass filtercircuit 320. In addition, where phase synchronization circuit 340includes digital interpolators, the implementation delay is augmented toaccount for the time delay caused by the digital interpolators.

In some cases, automatic gain control for learning and adjusting theamplitude level of detected signal 380 is accomplished using bandpassfilter circuit 320. In particular, for each servo gate, servo block mayreport the peak or maximum value at the output of bandpass filtercircuit 320 where region 249 becomes zero as the head assembly movesaway from spiral reference pattern 210. Depending upon the peak valuedetected, a user may change a gain value maintained in the register ofthe read channel to modify amplification/attenuation of detected signal380. This may be done in place of traditional adaptive solutions basedon least mean squared error approaches that may not work due to theramping up and down behavior of detected signal 380.

Turning to FIG. 4 b, an exemplary filter 311 that may be used in placeof notch filter 310 is depicted in accordance with one or moreembodiments of the present invention. Filter 311 includes a series offour flip-flops 312. The input of each of flip-flops 312 is fed by aninput signal 313 that is multiplied by a respective coefficient 317 in amultiplier 314, and added to the output of the preceding flip-flop usinga respective adder 318. The final flip-flop in filter 311 (i.e.,flip-flop 312 d) feeds an adder 319 that adds the output of flip-flop312 d to input 313 as multiplied by coefficient 317 e in a multiplier316 to create a filtered output 315. When included in system 300,filtered output 315 is provided to spiral entry locator circuit 330, andinput 313 is connected to detected signal 380.

Turning to FIG. 4 c, an exemplary filter 321 that may be used in placeof bandpass filter 320 is depicted in accordance with one or moreembodiments of the present invention. Filter 321 includes a series ofseven flip-flops 322. The input of each of flip-flops 322 is fed by aninput signal 323 that is multiplied by a respective coefficient 327 in amultiplier 324, and added to the output of the preceding flip-flop usinga respective adder 328. The final flip-flop in filter 321 (i.e.,flip-flop 322 g) feeds an adder 329 that adds the output of flip-flop312 g to input 323 as multiplied by coefficient 317 h in a multiplier326 to create a filtered output 325. When included in system 300,filtered output 325 is provided to spiral entry locator circuit 330,spiral exit locator circuit 350, and phase synchronization circuit 340.In addition, input 323 is connected to detected signal 380.

Turning to FIG. 4 d, an exemplary spiral entry detect circuit 331 thatmay be used in place of spiral entry detect circuit 330 is depicted inaccordance with one or more embodiments of the present invention. Theoutput of bandpass filter circuit 320 and the output of notch filtercircuit 310 are provided as inputs to a comparator 333. The output ofcomparator 333 indicates whether detected signal 380 is being receivedfrom spiral reference pattern 210, and is provided to a series of threeflip-flops 332, an AND gate 334 and an OR gate 335 that are used incombination to provide the time averaging and magnitude qualificationdiscussed above in relation to spiral entry locator circuit 330. Ofparticular note, AND gate 334 operates as a magnitude qualifier byrequiring three consecutive high assertions of output 391 before samplesare captured by spiral entry locator circuit 331. Another flip-flop 337and a multiplexer 336 is provided to maintain the detection of region229 once magnitude qualification is completed.

In particular, an output 338 of spiral entry detect 331 is initiallyasserted low causing the output from AND gate 334 to drive the input offlip-flop 337 via multiplexer 336. When the head assembly begins totraverse spiral reference pattern 210, an output 391 of comparator 333is asserted high indicating a tentative decision that region 229 hasbeen detected. Where output 391 remains high for three consecutiveperiods of the sample clock, all inputs to AND gate 334 are assertedhigh causing an output 339 of AND gate 339 to assert high. This, in turncauses output 338 to be asserted high on the subsequent sample clock andselection of the output of OR gate 335 to drive the input of flip-flop337. Upon a high assertion of output 338, spiral entry locator 331captures the subsequent N samples for comparison with samples capturedby spiral exit locator 350 as discussed above. The output of OR gate 335remains asserted high until output 391 is asserted low for fourconsecutive periods indicating that the head has finished traversingspiral reference pattern 210. At this point, output 339 is asserted lowand drives the input of flip-flop 337.

Turning to FIG. 4 e, a circuit 600 that may be used for implementingportions of spiral entry locator 330, spiral exit locator 350 andcomparator 360 is depicted in accordance with one or more embodiments ofthe present invention. Circuit 600 includes a series of three registers630 connected in series that are tailored for receiving and maintainingthe reference samples from region 229. It should be noted that wheremore than three reference samples are to be collected, additionalregisters 630 would be included; or where fewer than three referencesamples are to be collected, fewer registers 630 would be included. Whenenabled by an enable signal 615, registers 630 operate to receive andmaintain three consecutive samples of a detected signal 605 that is thefiltered version of detected signal 380. Enable signal 615 is initiallyasserted when output 338 is asserted, and disabled after threeconsecutive sample clocks.

Another series of registers 610 are connected in series and receive thesame detected signal 605. Registers 610 are continuously updated and theoutputs of registers 610 are compared in reverse order to the outputs ofregisters 630 using comparators 620. In particular, the output ofregister 610 c is compared with the output of register 630 a usingcomparator 620 c; the output of register 610 b is compared with theoutput of register 630 b using comparator 620 b; and the output ofregister 610 a is compared with the output of register 630 c usingcomparator 620 a. Again, where a different number of samples are to beused in determining the peak location, more or fewer of registers 610and comparators 620 may be used. The respective outputs of comparators620 are provided to an adder 640 that aggregates the received comparatoroutputs to create an error value. The error value is stored in aregister 650.

The stored error value in register 650 is compared with a previouslystored error value maintained in a register 660 using a comparator 670.A reset signal 645 is asserted each time processing of an overall signalpattern 219 begins to assure that register 660 is at a maximum, andregister 660 is only updated when a delay timer 625 is asserted (i.e.,the delay timer discussed in blocks 423, 425 of FIG. 3 above). An outputof comparator 670 controls the select input of a multiplexer 680. Inparticular, whenever the value in register 650 is less than the value inregister 660, the value from register 650 is fed to register 660 viamultiplexer 680. Alternatively, whenever the value in register 650 isgreater than the value in register 660, the value in register 660 is fedto register 660 via multiplexer 680. In this way, register 660 maintainsthe value of a minimum error 635 between the reference samples andsamples taken later in the processing of overall signal pattern 219.Further, while not shown in circuit 600, anytime the value from register650 is fed to register 660 via multiplexer 680, the time stampassociated with the value maintained in register 650 (i.e., the timestamp associated with the samples in registers 610 that were used tocreate the value stored in register 650) is updated as the time stamp ofthe minimum error output 635. This time stamp (i.e., T2 discussed inrelation to FIG. 3 above) is provided to location calculator 370.

Turning to FIG. 5, a low pass filter 500 that may be employed inrelation to one or more embodiments of the present invention isdepicted. Low pass filter 500 may be used to low pass filter detectedsignal 380 prior to providing it to spiral entry locator circuit 330and/or spiral exit locator circuit 350. Low pass filter 500 includes aseries of (N+1) flip-flops 550. The input of the first flip-flop in theseries (i.e., flip-flop 550 a) is by an input signal stream 512. Inturn, the output of flip-flop 550 a feeds the input of the succeedingflip-flop in the series (i.e., flip-flop 550 b). This continues with theoutput of each preceding flip-flop feeding the input of each succeedingflip-flop until flip-flop N (not shown) feeds the last flip-flop in theseries (i.e., flip-flop 550 h). The input signal stream 512 is added toan output 522 of low pass filter 500 by an adder 560, and the sum ofadder 560 is subtracted from the output of flip-flop 550 h to createoutput 522.

Other embodiments of the present invention may operate by identifyingthe region of increasing amplitude and taking two or more samples fromwithin the region. These two or more samples may be used to form a slopefor the region of increasing amplitude. In particular, the followingequation defines a straight line passing through the two or moresamples:y _(i) =m _(i) x _(i) +b _(i),where b is the y intercept and m is the slope of the region ofincreasing amplitude. The slope is defined by the following equation:m _(i)=(Y ₂ −Y ₁)/(X ₂ −X ₁),where (X₁, Y₁) and (X₂, Y₂) are sample points within the region ofincreasing amplitude. Thus, the straight line traversing the samplepoints is:y _(i)=[(Y ₂ −Y ₁)/(X ₂ −X ₁)]x _(i) +b _(i).

The process is continued by sampling through the transitional regionuntil the region of decreasing amplitude is identified. Once identified,two or more samples from within the region of decreasing amplitude aretaken. These samples are used to form a slope for the region ofdecreasing amplitude using the following equations:y _(d) =m _(d) x _(d) +b _(d); andm _(d)=(Y ₄ −Y ₃)/(X ₄ −X ₃),where (X₃, Y₃) and (X₄, Y₄) are sample points within the region ofdecreasing amplitude. The straight line traversing the sample points isthus:y _(d)=[(Y ₄ −Y ₃)/(X ₄ −X ₃)]x _(d) +b _(d).From this point, both of the aforementioned equations can be used tosolve for the intercept or peak time location. In particular, thesolution yields:

$\begin{matrix}{Peak} \\{Time} \\{Location}\end{matrix} = {\frac{\left( {b_{d} - b_{i}} \right)}{\left\lbrack {\left( {Y_{4} - Y_{3}} \right)/\left( {X_{4} - X_{3}} \right)} \right\rbrack - \left\lbrack {\left( {Y_{2} - Y_{1}} \right)/\left( {X_{2} - X_{1}} \right)} \right\rbrack}.}$Such calculations may be performed in a processor that may be includedwith one or more of the aforementioned embodiments.

Based on the disclosure provided herein, one of ordinary skill in theart will recognize a variety of advantages that are achievable usingvarious embodiments of the present invention. For example, embodimentsof the present invention may be used to aid a disk drive manufacturer inwriting their own servo patterns using a read channel coupled tocircuitry in accordance with one or more embodiments of the presentinvention. In some cases, embodiments of the present invention areimplemented in hardware and offer very quick operation. Otherembodiments of the present invention may be implemented in software orfirmware, or a combination of software/firmware and hardware forflexibility and/or cost effectiveness.

In conclusion, the present invention provides novel systems and methodsfor detecting peak signal location. While detailed descriptions of oneor more embodiments of the invention have been given above, variousalternatives, modifications, and equivalents will be apparent to thoseskilled in the art without varying from the spirit of the invention.Therefore, the above description should not be taken as limiting thescope of the invention, which is defined by the appended claims.

1. A method for peak signal detection, wherein the method comprises:receiving a signal, wherein the signal includes a first signal regionincreasing in amplitude and a second signal region decreasing inamplitude, and wherein the first signal region and second signal regionare coupled by a transitional signal region; sampling the first signalregion to yield a first plurality of samples corresponding to the firstsignal region; sampling the second signal region to yield a secondplurality of samples corresponding to the second signal region; fixing afirst time associated with one sample of the first plurality of samples;comparing the second plurality of samples with the one of the firstplurality of samples; identifying one of the second plurality of samplesthat is closest to the one of the first samples; fixing a second timeassociated with the one of the second plurality of samples; andcalculating a midpoint between the first time and the second time,wherein the mid-point corresponds to the peak of the signal.
 2. Themethod of claim 1, wherein identifying the second time includes: storingthe second plurality of sequential samples; subtracting the firstplurality of sequential samples from the second plurality of sequentialsamples on a sample by sample basis to yield a number of differences;and summing the absolute value of each of the differences to yield anabsolute difference.
 3. The method of claim 2, wherein identifying thesecond time further includes: repeating the storing the second pluralityof sequential samples, and the subtracting the first plurality ofsequential samples from the second plurality of sequential samples on asample by sample basis and in reverse order at least until a minimumabsolute difference is identified.
 4. The method of claim 1, wherein themethod further comprises: providing a storage medium, wherein thestorage medium includes a spiral reference pattern; providing a headassembly disposed in relation to the storage medium; and whereinreceiving the signal includes traversing the storage medium by the headassembly along a traversal path, wherein the traversal path crosses thespiral reference pattern at an angle greater than zero, wherein thefirst signal region occurs in relation to an increasing cross-over withthe spiral reference pattern, wherein the second signal region occurs inrelation to a decreasing cross-over with spiral reference pattern, andwherein the transitional signal region occurs in relation to asubstantially constant cross-over with the spiral reference pattern. 5.The method of claim 1, wherein the method further includes: applyingdigital interpolation, wherein the digital interpolation is operable toproduce the first plurality of sequential samples and the secondplurality of sequential samples in phase with the peaks of informationmaintained in the spiral reference pattern.
 6. The method of claim 1,wherein the angle at which the traversal path crosses the spiralreference pattern is programmable.
 7. A method for identifying signalpeaks of a spiral reference pattern, the method comprising: providing astorage medium, wherein the storage medium includes the spiral referencepattern; traversing the storage medium along a traversal path, whereinthe traversal path crosses the spiral reference pattern at an anglegreater than zero, wherein the traversal results in receiving a signal,and wherein the signal includes a first signal region, a second signalregion, and a transitional signal region; sampling the first signalregion to form a first sample; identifying a first location within thefirst signal region; fixing a first time associated with the firstsample; identifying a second location within the second signal region,wherein a difference between the first sample and a second sampleassociated with the second location is a minimum; fixing a second timeassociated with the second sample; based at least in part on the firsttime and the second time, calculating a distance between the firstlocation and the second location; determining a peak of the signal,wherein the peak of the signal is approximately equal distance from thefirst signal region and the second signal region; and wherein the firstsignal region occurs in relation to an increasing cross-over with thespiral reference pattern, wherein the second signal region occurs inrelation to a decreasing cross-over with spiral reference pattern,wherein the transitional signal region occurs in relation to asubstantially constant cross-over with the spiral reference pattern, andwherein the first signal region is substantially symmetric with thesecond signal region.
 8. The method of claim 7, wherein the methodfurther comprises: providing a storage medium, wherein the storagemedium includes a spiral reference pattern; providing a head assemblydisposed in relation to the storage medium; and wherein receiving thesignal includes traversing the storage medium by the head assembly alonga traversal path, wherein the traversal path crosses the spiralreference pattern at an angle greater than zero, wherein the firstsignal region occurs in relation to an increasing cross-over with thespiral reference pattern, wherein the second signal region occurs inrelation to a decreasing cross-over with spiral reference pattern, andwherein the transitional signal region occurs in relation to asubstantially constant cross-over with the spiral reference pattern. 9.The method of claim 7, wherein the method further includes: applyingdigital interpolation, wherein the digital interpolation is operable toproduce the first plurality of sequential samples and the secondplurality of sequential samples in phase with the peaks of informationmaintained in the spiral reference pattern.
 10. The method of claim 7,wherein the angle at which the traversal path crosses the spiralreference pattern is programmable.